1. Field of the Invention
This invention relates to an amplification device that has a distortion detection loop and distortion removal loop, and that compensates for the distortion that arises in an amplifier due to a feedforward scheme, and particularly to an amplification device intended to reduce costs.
2. Description of the Prior Art
For example, in base stations provided for mobile communications systems, when the signal subject to transmission is amplified with an amplifier, compensation for the distortion that arises in such an amplifier is performed in order to achieve wireless communication with minimal distortion while satisfying the radio regulations for leak power in adjacent channels and the like. In addition, one example of an amplification device used to perform the compensation of distortion is an amplification device that performs distortion compensation by means of the feedforward (FF) scheme.
FIG. 6 shows an example of the constitution of an amplification device that performs distortion compensation by means of the feedforward scheme.
With the amplification device shown in the figure, in the distortion detection loop, a directional coupler 71 divides the analog signal in the radio frequency (RF) band input from the input terminal P and subject to amplification, and a main amplifier 72 amplifies one branch of the divided signal while a delay line 73 delays the other branch of the divided signal, and a directional coupler 74 takes the amplified signal from the main amplifier 72 and subtracts the delayed other branch of the divided signal to detect the distortion arising in the main amplifier 72. Here, the delay line 73 adjusts the timing of the processing of one branch of the divided signal and the other branch of the divided signal so that the distortion arising in the main amplifier 72 is detected by the directional coupler 74.
In addition, with the amplification device shown in the figure, in the distortion removal loop, the signal amplified by the main amplifier 72 is delayed by a delay line 75 and the distortion detected by the distortion detection loop is amplified by an auxiliary amplifier 76. A directional coupler 77 takes this delayed amplified signal from the main amplifier 72 and subtracts the amplified signal from the auxiliary amplifier 76 to obtain an amplified signal after compensation for the distortion in the amplified signal by the main amplifier 72 where the distortion components are reduced. This distortion-compensated amplified signal is then output from an output terminal Q. Here, the delay line 75 adjusts the timing of the processing of the signal amplified by the main amplifier 72 and the distortion detected by the distortion detection loop so that the distortion components in the signal amplified by the main amplifier 72 are removed.
Here, an example of the prior art is indicated by the circuit consisting of a modulator and the like as a distortion compensation circuit that uses a combination of a feedforward scheme and a pre-distortion scheme in the xe2x80x9cdistortion compensation circuitxe2x80x9d recited in the publication of unexamined Japanese patent application (Kokai) No. JP-A-2000-212116 and in the circuit consisting of a delay circuit and the like as a pre-distortion scheme-based distortion compensation circuit that uses an image rejection-type frequency modulator in an up-converter and down-converter in the xe2x80x9cbase station used for wireless communicationxe2x80x9d recited in the publication of unexamined Japanese patent application (Kokai) No. JP-A-9-64780. Note that each of the techniques recited in the literature differ from the constitution and object of the present invention as recited hereinafter.
However, with a conventional amplification device based on the feedforward scheme as illustrated in FIG. 6 above, the distortion detection loop is constituted by using a coaxial cable or filter or other delay means to delay harmonically the signal in the wireless frequency band, so there are problems in that a relatively large device footprint is required and achieving low costs is difficult.
The present invention is intended to solve these problems in the prior art and has as its object to provide an amplification device that has a distortion detection loop and distortion removal loop, and that can achieve low costs when compensating for the distortion that arises in an amplifier due to a feedforward scheme.
In order to achieve the aforementioned object, the amplification device according to the present invention has a distortion detection loop that amplifies the signal subject to amplification with an amplifier and detects the distortion arising in said amplifier, and a distortion removal loop that removes the distortion detected by the distortion detection loop from the signal amplified by said amplifier, and the distortion detection loop and distortion removal loop compensate for the distortion that arises in said amplifier by means of a feedforward scheme, based on a distortion detection loop constituted as follows.
To wit, in the distortion detection loop, among the two branches of the digital baseband signal subject to amplification that is divided into two, a first digital modulation means uses one branch of the digital baseband signal to modulate a carrier signal, an amplifier amplifies the modulated signal obtained from the first digital modulation means, delay means delays the other branch of the digital baseband signal, a second digital modulation means that uses the other branch of the digital baseband signal delayed by the delay means to modulate a carrier signal, phase-change means changes the phase of the modulated signal obtained from the second digital modulation means, and distortion detection means detects the distortion arising in said amplifier from the signal amplified by the amplifier and the modulated signal whose phase is changed by the phase-change means.
Accordingly, for example, if a constitution is adopted such that a baseband signal in a frequency band lower than the wireless frequency band (the other digital baseband signal) is subject to delay by the delay means of the distortion detection loop and this baseband signal is converted to a signal in the wireless frequency band by means of modulation of the carrier frequency of the wireless frequency band after this delay, it is possible to achieve a smaller device footprint and lower cost than in the prior art, for example. In addition, because the constitution is such that a digital baseband signal is delayed, it is possible to achieve lower costs by the conversion to digital and the adjustment of the delay time can be automated to simplify the work of adjusting this delay time.
Here, various signals may be used as the signal subject to amplification, as signals subject to wireless transmission may be used, for example.
In addition, amplifiers of various constitutions may be used.
In addition, amplifiers typically suffer from intermodulation distortion and other types of distortion when amplifying signals.
In addition, various levels of precision may be used as the precision of detection of distortion by the distortion detection loop as long as they are of a degree that is effective in practical use, for example.
In addition, various levels of precision may be used as the precision of removal of distortion by the distortion removal loop (to wit, the precision of compensation for distortion) as long as they are of a degree that is effective in practical use, for example.
In addition, the digital baseband signal used may be, for example, a baseband frequency band which is a digital signal consisting of an I component and a Q component.
In addition, various signals may be used as the carrier signal used by the first digital modulation means and the carrier signal used by the second digital modulation means.
In addition, various modulation schemes may be used as the modulation scheme used by the first digital modulation means and the modulation scheme used by the second digital modulation means.
Note that the same modulation processing may be performed using the same carrier signal and the same modulation scheme in both the first digital modulation means and the second digital modulation means, for example.
In addition, the modulated signal obtained from the first digital modulation means and the modulated signal obtained from the second digital modulation means may be analog signals, for example.
In addition, various degrees of delay may be used as the degree of delaying the other digital baseband signal by means of the delay means; for example, a degree of delay may be used such that it is possible to adjust the timing of processing of one branch of the divided signal (one digital baseband signal or one modulated signal) and the other branch of the divided signal (the other digital baseband signal or the other modulated signal) so that the distortion arising in the amplifier is (appropriately) detected by the distortion detection means.
In addition, a digital delay circuit may be used as the delay means, for example.
In addition, various degrees may be used as the degree of changing the phase of the modulated signal by the phase-change means; for example, a degree of phase change may be used such that the phase relationship between one branch of the divided signal (one digital baseband signal or one modulated signal) and the other branch of the divided signal (the other digital baseband signal or the other modulated signal) so that the distortion arising in the amplifier is (appropriately) detected by the distortion detection means.
In addition, in the distortion detection means, by taking the signal amplified by the amplifier and subtracting the modulated signal whose phase is changed by the phase-change means, the distortion arising in said amplifier may be detected, for example. To wit, in general, the signal amplified by the amplifier contains signal components subject to amplification and distortion components arising in said amplifier, and the modulated signal whose phase is changed by the phase-change-means contains only the signal components subject to amplification, so by taking the difference between these, it is possible to obtain the distortion components arising in the amplifier.
In addition, in one sample configuration, the distortion detection loop is provided with a division means that divides the digital baseband signal subject to amplification into two. In this configuration, one branch of the divided signal produced by the division means is processed by the first digital modulation means as one digital baseband signal while the other branch of the divided signal is processed by the delay means as the other branch of the digital baseband signal. Note that the division means may be constituted by means of a divider or directional coupler that bisects the signal, for example, or by using wiring or the like that bisects the signal, for example.
In addition, the amplification device according to the present invention has a distortion detection loop that amplifies the signal subject to amplification with an amplifier and detects the distortion arising in said amplifier, and a distortion removal loop that removes the distortion detected by the distortion detection loop from the signal amplified by said amplifier, and the distortion detection loop and distortion removal loop compensate for the distortion that arises in said amplifier by means of a feedforward scheme, based on a distortion detection loop constituted as follows.
To wit, in the distortion detection loop, a digital filter filters the digital baseband signal subject to amplification, division means divides into two the digital baseband signal filtered by the digital filter, digital modulation means performs modulation with one branch of the digital baseband signal divided by the division means, an amplifier amplifies the modulated signal obtained from the digital modulation means, D/A conversion means converts the other branch of the digital baseband signal to an analog baseband signal, delay means delays the analog baseband signal obtained from the D/A conversion means, analog modulation means performs modulation by means of the analog baseband signal delayed by the delay means, phase-change means changes the phase of the modulated signal obtained from the analog modulation means, and distortion detection means detects the distortion arising in said amplifier from the signal amplified by the amplifier and the modulated signal whose phase is changed by the phase-change means.
Accordingly, for example, if a constitution is adopted such that a baseband signal in a frequency band lower than the wireless frequency band (the analog baseband signal) is subject to delay by the delay means of the distortion detection loop and this baseband signal is converted to a signal in the wireless frequency band by means of modulation of the carrier frequency of the wireless frequency band after this delay, it is possible to achieve a smaller device footprint and lower cost than in the prior art, for example.
Here, the digital filter used may be, for example, one that has filtering characteristics that limit the bandwidth of the digital baseband signal subject to amplification.
In addition, various means may be used as the division means.
In addition, various modulation schemes may be used in the digital modulation means.
In addition, various modulation schemes may be used in the analog modulation means.
Note that the same modulation processing may be performed using the same modulation scheme so that the same modulated signal is obtained in both the digital modulation means and the analog modulation means, for example.
In addition, the modulated signal obtained from the digital modulation means and the modulated signal obtained from the analog modulation means may be an analog signal, for example.
In addition, various degrees of delay may be used as the degree of delaying the analog baseband signal by means of the delay means; for example, a degree of delay may be used such that it is possible to adjust the timing of processing of one branch of the divided signal and the other branch of the divided signal so that the distortion arising in the amplifier is (appropriately) detected by the distortion detection means.
In addition, an analog delay circuit may be used as the delay means, for example.
In addition, various degrees may be used as the degree of changing the phase of the modulated signal by the phase-change means; for example, a degree of phase change may be used such that the phase relationship between one branch of the divided signal and the other branch of the divided signal so that the distortion arising in the amplifier is (appropriately) detected by the distortion detection means.
Here follows another sample configuration of the amplification device according to the present invention.
The amplification device according to the present invention has a distortion detection loop that amplifies the signal subject to amplification with an amplifier and detects the distortion arising in said amplifier, and a distortion removal loop that removes the distortion detected by the distortion detection loop from the signal amplified by said amplifier, and the distortion detection loop and distortion removal loop compensate for the distortion that arises in said amplifier by means of a feedforward scheme, based on a distortion detection loop constituted as follows.
To wit, a digital filter filters the digital baseband signal subject to amplification, division means divides into two the digital baseband signal filtered by the digital filter, a first D/A conversion means converts one branch of the digital baseband signal divided by the division means to an analog baseband signal, a first analog modulation means performs modulation with the analog baseband signal obtained from the first D/A conversion means, an amplifier amplifies the modulated signal obtained from the first analog modulation means, a second D/A conversion means converts the other branch of the digital baseband signal to an analog baseband signal, delay means delays the analog baseband signal obtained from the second D/A conversion means, the second analog modulation means performs modulation by means of the analog baseband signal delayed by the delay means, phase-change means changes the phase of the modulated signal obtained from the second analog modulation means, and distortion detection means detects the distortion arising in said amplifier from the signal amplified by the amplifier and the modulated signal whose phase is changed by the phase-change means.
Accordingly, for example, if a constitution is adopted such that a baseband signal in a frequency band lower than the wireless frequency band (the analog baseband signal) is subject to delay by the delay means of the distortion detection loop and this baseband signal is converted to a signal in the wireless frequency band by means of modulation of the carrier frequency of the wireless frequency band after this delay, it is possible to achieve a smaller device footprint and lower cost than in the prior art, for example.
Note that the same modulation processing may be performed using the same modulation scheme in both the first analog modulation means and the second analog modulation means, for example.
In addition, an analog delay circuit may be used as the delay means, for example.
In addition, with the amplification device according to the present invention, in the event that there is no need to perform the adjustment of the phase relationship among the two signals by means of the aforementioned phase-change means, it is possible to use a configuration wherein the distortion detection loop does is not provided with a phase-change means. In this configuration, the distortion detection loop is provided with a distortion detection means that detects the distortion arising in this amplifier from the signal amplified by the amplifier and the modulated signal (the modulated signal obtained from the second digital modulation means, the modulated signal obtained from the analog modulation means, or the modulated signal obtained from the second analog modulation means).
The amplification device according to the present invention compensates for the distortion that arises in said amplifier by means of a feedforward scheme, based on a distortion detection loop constituted as follows.
To wit, the distortion removal means is constituted using delay means that delays the signal amplified by the amplifier of the distortion detection loop, a distortion amplifier that amplifies the distortion detected by the distortion detection means of the distortion detection loop and distortion removal means that removes the signal amplified by the distortion amplifier from the amplified signal delayed by the delay means. Moreover, in the distortion removal loop, the delay means delays the signal amplified by the amplifier of the distortion detection loop, the distortion amplifier amplifies the distortion detected by the distortion detection means of the distortion detection loop and the distortion removal means removes the signal amplified by the distortion amplifier from the amplified signal delayed by the delay means.
Here, amplifiers of various constitutions may be used as the distortion amplifier.
In addition, in the distortion removal means, by taking the amplified signal delayed by the delay means and subtracting the signal amplified by the distortion amplifier, the distortion components contained in said delayed amplified signal are diminished. Note that this delayed amplified signal corresponds to the signal amplified by the amplifier of the distortion detection loop, and this signal amplified by the distortion amplifier corresponds to a signal in which the distortion detected by the distortion detection loop is amplified.
In addition, with the amplification device according to the present invention, as one sample configuration, a delay filter is used as the delay means of the distortion removal loop.
In this configuration, when processing signals in high frequency bands for example, it is possible to make the device compact and also diminish losses on the output side of distortion-compensated amplified signals.
In addition, the amplification device according to the present invention as described above is suitable for use in a base station provided in a mobile communications system, for example.
To wit, with a base station according to the present invention, the amplification device according to the present invention as described above is provided and signals subject to transmission to mobile stations are amplified by said amplification device and transmitted wirelessly.
Here, various systems are applicable as the mobile communications systems; for example, cellular phone systems and Personal Handy phone Systems (PHS) are applicable.
In addition, various communication protocols can be used as the communication protocol; for example, Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) or other communications protocols may be used.